Falling (8)
I believe the answer is:
tumbling
'falling' is the definition.
(tumbling is a kind of falling)
This is all the clue.
(Other definitions for tumbling that I've seen before include "Falling down, as if collapsing" , "Acrobatics" , "Rolling over and over, as a gymnast might" , "Falling headlong" , "Quickly declining" .)